In recent years, due to societal demand for protection of environment and nature, research on fuel cells as a highly efficient and clean energy source is being actively conducted. Among others, expectations are growing for polymer electrolyte fuel cells (PEFC) and hydrogen internal combustion engines as an energy source for 0household and onboard purposes because of their advantages in low temperature operation and high output density.
In these systems, because hydrogen, which is a flammable gas, is used as fuel, for example, detection of gas leakage is cited as one of important issues.
In a known flammable gas detection apparatus for detecting the gas concentration of flammable gas of this type existing in an atmosphere for detection, a gas detection element is disposed in the atmosphere for detection, where the gas detection element is provided with a heating resistor whose resistance value is changed by its own temperature change (heat generation), and with a temperature-measuring resistor whose resistance value is changed by a change in environment temperature.
Specifically, in this flammable gas detection apparatus, the resistance value of the heating resistor of the gas detection element is controlled by a bridge circuit to have resistance values corresponding to two set temperatures (a first set temperature and a second set temperature), and the gas concentration is calculated by using a control voltage (voltage across the heating resistor) at the time and a voltage difference (temperature voltage) caused by a change in the resistance value of the temperature-measuring resistor.
Each of the set temperatures (the first set temperature and the second set temperature) is changed by selectively switching the conduction states of fixed resistors with different resistance values installed in the bridge circuit at regular periods of time, for example (see Patent Document 1, for example). Thus, the voltage across the heating resistor at the first set temperature and the second set temperature can be detected by using a single bridge circuit and heating resistor, whereby the size of the gas detection element can be decreased and power consumption can be suppressed.
Patent Document 1 describes that, in consideration of the variation of the concentration of the flammable gas in the atmosphere for detection depending on the humidity in the atmosphere for detection, in addition to the voltage difference, the ratio (voltage ratio) of the voltages across the heating resistor at the first set temperature and the second set temperature is computed, and the gas concentration is corrected by utilizing the fact that the ratio is substantially proportional to the humidity.